Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 NANO EXPRESS Open Access Preparation, characterization and photocatalytic behavior of WO3-fullerene/TiO2 catalysts under visible light Ze-Da Meng, Lei Zhu, Jong-Geun Choi, Chong-Yeon Park and Won-Chun Oh* Abstract WO3-treated fullerene/TiO2 composites (WO3-fullerene/TiO2) were prepared using a sol-gel method The composite obtained was characterized by BET surface area measurements, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and UV-vis analysis A methyl orange (MO) solution under visible light irradiation was used to determine the photocatalytic activity Excellent photocatalytic degradation of a MO solution was observed using the WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 composites under visible light An increase in photocatalytic activity was observed, and WO3-fullerene/TiO2 has the best photocatalytic activity; it may attribute to the increase of the photo-absorption effect by the fullerene and the cooperative effect of the WO3 Introduction Textile manufacturing involves several processes which generate large quantities of wastewaters These effluents are highly variable in composition with relatively low biochemical oxygen demand and high chemical oxygen demand contents and are typically characterized as follow: first: strong color due to residual dyes, second: recalcitrance due to the presence of compounds such as dyes, surfactants, and sizing agents; and third: high salinity, high temperature, and variable pH [1-3] The textile effluents effective treatment usually requires a combination of various physical, chemical, and biological technologies Some studies researched the treatment of model solutions containing various commercial dyes with emphasis on azo dyes since these are extensively used in dyeing processes These azo dye molecules are chemically stable and hardly biodegradable aerobically Most attention has been paid on the oxidative degradation of MB and MO representative mono-azo dyes by oxidation processes [4,5] TiO2 is the most widely used photocatalyst far effective decomposition of organic compounds in air and water under irradiation of UV light with wavelength shorter than corresponding to its * Correspondence: wc_oh@hanseo.ac.kr Department of Advanced Materials Science & Engineering, Hanseo University, Seosan, Chungnam, 356-706, South Korea band gap energy, due to its relatively high photocatalytic activity, biological and chemical stability, low cost, nontoxic nature, and long-term stability However, the photocatalytic activity of TiO2 (the band gap of anatase TiO is 3.2 eV and it can be excited by photons with wavelengths below 387 nm) is limited to irradiation wavelengths in the UV region [6,7] However, only about 3% to 5% of the solar spectrum falls in this UV range This limits the efficient utilization of solar energy for TiO2 Some problems still remain to be solved in its application, such as the fast recombination of photogenerated electron-hole pairs Therefore, improving photocatalytic activity by modification has become a hot topic among researchers in recent years [8,9] For the improvement of the photocatalytic activity of TiO2, TiO2 has been coupled with other semiconductors such as SnO [10] which can induce effective charge separation by trapping photogenerated electrons TiO coupled with other semiconductors has been reported to perform both the abovementioned functions This has been realized by coupling the WO3 [11] semiconductor with TiO Because of its band gap (E g = 2.6 eV to approximately 3.0 eV) [12], WO3 mainly absorbs in the near ultraviolet and blue regions of the solar spectrum As a basic function, WO3 has a suitable conduction band potential to allow the transfer of photogenerated electrons from TiO2 facilitating effective charge separation © 2011 Meng et al; licensee Springer This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 However, in practical applications, the photoelectrical properties and photocatalytic efficiency of WO3 require improvement C60 has attracted considerable interest for its interesting properties owing to the delocalized conjugated structures and electron-accepting ability One of the most remarkable properties of C60 in electron-transfer processes is that it can efficiently arouse rapid photoinduced charge separation and relatively slow charge recombination [13] Therefore, a combination of photocatalysts and C 60 might provide an ideal system to achieve enhanced charge separation by photoinduced electron transfer Some fullerene-donor linked molecules on an electrode were reported to exhibit excellent photovoltaic effects upon photo-irradiation A conjugated two-dimensional π-system is suitable not only for synthetic light-harvesting systems but also for efficient electron transfer because the uptake or release of electrons results in minimal structural and solvation change upon electron transfer Fullerenes contain an extensively conjugated three-dimensional π-system and are described as having a closed-shell configuration consisting of 30 bonding molecular orbitals with 60 π-electrons This material is also suitable for efficient electron-transfer reduction because of the minimal changes in structure and salvation associated with electron transfer [14,15] Unfortunately, deposited metal particles or coupled with other semiconductors only serve as electron trapping agent, or transfer of photogenerated electrons and are not effective to enhance the adsorption of the pollutants Fullerene-treated TiO2 coupled with other semiconductors has been reported to perform both the abovementioned functions [16] In addition, C60 is one of the promising materials because of its band gap energy, about 1.6 to 1.9 eV It has strong absorption in the ultraviolet region and weak but significant bands in the visible region In general, the coupled systems exhibit higher degradation rate as well as the increased extent of degradation [17] The studies for comparing the coupled semiconductors with visible light, however, are scarce In this paper, WO 3-treated fullerene, fullerene-supported TiO2, and WO3-fullerene/TiO2 were synthesized and exhibited enhanced vis-photocatalytic activities compared to the pure TiO2 This study focused on the Page of 11 fabrication and characterization of WO3-fullerene/TiO2 composite in a preparation procedure Structure variations, surface state, and elemental compositions were examined for the preparation of WO3 -fullerene/TiO composites X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and UV-visible (UV-vis) were used to characterize these new photocatalysts The catalytic efficiency of the WO3-fullerene/ TiO2 composite was evaluated by the photo degradation of methyl orange (MO, C14H14N3NaO3S) Materials Benzene (99.5%) and ethyl alcohol were purchased as reagent-grade from Duksan Pure Chemical Co (Ansan-si, Gyeonggi-do, South Korea) and Daejung Chemical Co (Gwangju-si, Gyeonggi-do, South Korea) and were used as received Crystalline fullerene [C 60] powder (99.9% purity from Tokyo Kasei Kogyo Co Ltd., Tokyo, Japan) was used as the carbon matrix Titanium(IV) n-butoxide (TNB, C 16 H 36 O Ti) as the titanium source for the preparation of the WO3-fullerene/TiO composites was purchased as reagent-grade from Acros Organics (Morris Plains, NJ, USA) The ammonium metatungstate hydrate (H 26 N O 40 W 12 ·xH O) purchased from Sigma-Aldrich™ Chemie GmbH (Steinheim, Germany) was used as a raw material to generate WO at high temperatures Methyl orange (MO, C 14 H 14 N NaO S, 99.9%, Duksan Pure Chemical Co., Ltd) was of analytical grade Preparation of WO3-fullerene composites MCPBA (m-chloroperbenzoic acid, ca g) was suspended in 50 ml benzene, followed by the addition of fullerene (ca 30 mg) The mixture was heated under reflux in air and stirred for h at 343 K The solvent was then dried at the boiling point of benzene (353.13 K) After completion, the dark brown precipitates were washed with ethyl alcohol and dried at 323 K, resulting in the formation of oxidized fullerene For WO3 coating, 3.8 × 10-5 mol H26N6O40W12·xH2O was added to 50 ml of distilled water (shown in Table 1) The resulting mixture was heated under reflux in air and stirred at 343 K for h using a magnetic stirrer in a vial After heat treatment at 773 K for h, the WO -fullerene compounds were formed Table Nomenclature of the samples prepared with the photocatalysts Preparation method -5 Nomenclatures 3.8 × 10 mol H26N6O40W12·xH2O + H2O + MCPBA + 30 mg fullerene WO3-fullerene MCPBA+ benzene + 30 mg fullerene + ml TNB Fullerene-TiO2 MCPBA+ benzene + 30 mg fullerene + 3.8 × 10-5 mol H26N6O40W12·xH2O + H2O + benzene + ml TNB WO3-fullerene/TiO2 Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Preparation of WO3-fullerene/TiO2 composites WO3-fullerene was prepared using pristine concentrations of TNB for the preparation of WO3-fullerene/TiO2 composites WO3-fullerene powder was mixed with ml TNB The solutions were homogenized under reflux at 343 K for h, while being stirred in a vial After stirring, the solution transformed to WO -fullerene/TiO gels and heat treated at 873 K to produce the WO3-fullerene/TiO2 composites Characterization of photocatalysts compounds To measure the structural variations, XRD patterns were obtained using an X-ray generator (Shimadzu XD-D1, Shimadzu Corporation, Kyoto, Japan) with Cu Ka radiation Scanning electron microscopy (SEM, JSM-5200, JEOL, Tokyo, Japan) was used to observe the surface state and structure of the photocatalyst composites Energy dispersive X-ray spectroscopy (EDX) was also used for elemental analysis of the samples The specific surface area (BET) was determined by N adsorption measurements at 77 K (Monosorb, Quantachrome Instruments Ltd, Boynton Beach, FL, USA) Transmission electron microscopy (TEM, JEM-2010, JEOL) was used to observe the surface state and structure of the photocatalyst composites at an acceleration voltage of 200 kV TEM was also used to examine the size and distribution of the titanium and iron particles deposited on the fullerene surface of various samples The TEM specimens were prepared by placing a few drops of the sample solution on a carbon grid UV-vis diffused reflectance spectra were obtained using a UV-vis spectrophotometer (Neosys-2000, Scinco, Seoul, South Korea) by using BaSO as a reference and were converted from reflection to absorbance by the Kubelka-Munk method Photocatalytic degradation of MO The photocatalytic activities were evaluated by MO degradation in aqueous media under visible light irradiation For visible light irradiation, the reaction beaker was located axially and held in a visible lamp (8 W, halogen lamp, KLD-08L/P/N, Fawoo Technology, Bucheon Si, South Korea) box The luminous efficacy of the lamp is 80 lm/W, and the wavelength is 400 nm to approximately 790 nm The lamp was used at a distance of 100 mm from the aqueous solution in a dark box The initial concentration of the MO was set at × 10-5 mol/L in all experiments The amount of the photocatalysts (WO -fullerene, fullerene-TiO , and WO -fullerene/ TiO ) composite was 0.05 g per 50 ml solution The reactor was placed for h in the darkness box in order to make the photocatalyst composites particles adsorbed the MO molecule maximum After the adsorption state, the visible light irradiation was restarted to make the degradation reaction proceed In the process of Page of 11 degradation of methyl orange, a glass reactor (diameter = cm, height = cm) was used and the reactor was placed on the magnetic churn dasher The suspension was then irradiated with visible light for a set irradiation time Visible light irradiation of the reactor was done for 10, 30, 60, 90, and 120 min, respectively Samples were withdrawn regularly from the reactor and dispersed powders were removed by a centrifuge The clean transparent solution was analyzed by UV/vis spectroscopy The MO concentration in the solution was determined as a function of the irradiation time Elemental analysis of the preparation Figure shows the EDX patterns of the WO3 -treated fullerene, fullerene-supported TiO2, and WO3-fullerene/ TiO2 EDX indicated C, O, Ti, and W as the major elements in the composites Table lists the numerical results of EDX quantitative microanalysis of the samples Figure 1c shows the presence of C, O, and Ti, as major elements with strong W peaks There were some small impurities, which were attributed to the use of fullerene without purification In most samples, carbon and titanium were present as major elements with small quantities of oxygen in the composite Surface characteristics of the samples Table lists the specific surface area (BET) of the materials examined The BET surface area of pure TiO2 was 18.95 m2/g, and the surface area of pure fullerene was 85.05 m2/g Tungsten oxide particles were introduced into the pores of fullerene, which decreased the BET surface area The surface area of fullerene-TiO was 64.62 m2/g Fullerene contains many pores, which can increase the surface area of the photocatalyst The BET surface area decreased from 85.05 m2/g for pure fullerene to 57.74 m2 /g for WO3 -fullerene/TiO2 This suggests that the TiO2 and tungsten oxide were introduced into the pores of the fullerenes, which decreased the BET surface area The WO 3-fullerene sample had the largest surface area, which can affect the adsorption reaction The micro-surface structures and morphology of the fullerene-TiO2, WO3-fullerene, and WO3-fullerene/TiO2 composites were characterized by SEM (Figure 2) SEM is used for inspecting topographies of specimens at very high magnifications using a piece of equipment called the scanning electron microscope Figure shows the macroscopic changes in the morphology of the WO3fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 In Figure 2a, WO3-fullerene has the small particle size and a good dispersion The fullerene particles were spherical particles in shape with small facets, and fullerene has a good dispersion [18] For the fullerene-TiO sample (Figure 2b), the fullerene particles were well attached to Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page of 11 (a) (b) (c) Figure EDX elemental microanalysis of WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 the TiO2 surface with a uniform distribution, but the particle size is bigger than WO3-fullerene Zhang et al reported that a good dispersion of small particles could provide more reactive sites for the reactants than aggregated particles [19] At the same time, the conductivity of fullerene can facilitate electron transfer between the adsorbed dye molecules and catalyst substrate With the WO3-fullerene/TiO2 samples (Figure 2c), tungsten particles were fixed to the TiO2 surface and fullerene particles in some spherical particles, but the distribution was Table EDX elemental microanalysis, BET surface area, and kapp values of photocatalysts Sample name C (%) O (%) W (%) Impurity (%) C60 99.99 - - TiO2 - - - WO3-fullerene 54.08 17.25 Fullerene-TiO2 27.24 WO3-fullerene/TiO2 10.41 kapp Ti (%) BET (m2/g) 0.01 - 85.05 - 0.01 99.99 18.95 2.24 × 10-4 22.92 5.75 - 73.25 2.86 × 10-3 36.71 - 0.02 58.82 64.62 1.52 × 10-3 35.28 3.22 1.03 50.06 57.74 4.75 × 10-3 Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page of 11 (a) (b) (c) Figure SEM images of WO3-fullerene (a), fullerene-TiO2 (b), and WO3-fullerene/TiO2 (c) not uniform There was no clear difference in the intensity of aggregation Because of the aggregation, fullerene cannot show clearly The particles were strongly aggregated and that discrete particles were impossible to find so the average particle size was difficult to obtain It may be that particles with similar or close crystallographic orientations were formed bulky crystal or quasicrystals with modulated surfaces and regular shapes Figure shows TEM images of the WO -fullerene/ TiO2 composites TEM is a technique used for analyzing the morphology, crystallographic structure, and even compositing of a specimen As shown in Figure 3, particles were observed upon enlargement of the images This indicates that the surface of the WO3 particles is cleaned under exposure to the reaction conditions Figure shows large clusters with an irregular agglomerated Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page of 11 Figure TEM image of the WO3-fullerene/TiO2 composites dispersion of TiO2 Fullerene were distributed uniformly outside the surface of the TiO2 nanoparticles with a size of approximately 10 to 20 nm, and WO3 were distributed uniformly over the surface of the fullerene and TiO , even though this caused partial agglomeration to form block particles TEM also revealed the presence of metal nanoparticles on the fullerene particles Structural analysis XRD was used to determine the crystallographic structure of the inorganic component of the composite Figure shows the XRD patterns of the WO -treated fullerene, fullerene-supported TiO2, and WO3-fullerene/ TiO2 In Figure 4, A is anatase and W is the monoclinic phase of tungsten oxide The structure of WO3-fullerene composites showed monoclinic phase of tungsten oxide The peaks at 23.15°, 23.61°, 24.37°, 26.61°, 33.33°, 33.65°, 34.01°, 41.51°, 44.88°, 47.22°, 49.32°, 50.48°, 53.46°, and 55.11° 2θ were assigned to diffraction planes of (001), (020), (200), (120), (111), (021), (201), (220), (221), (131), (002), (400), (112), (022), and (401) of monoclinic WO3 phase [20,21] WO3-fullerene/TiO2 and fullerene-TiO2 showed anatase phase of TiO2 The crystal structure of TiO2 is determined mainly by the heat-treated temperature The peaks at 25.3°, 37.5°, 48.0°, 53.8°, 54.9°, and 62.5° 2θ were assigned to the (101), (004), (200), (105), (211), and (204) planes of anatase [22-24], indicating the developed fullerene/TiO2 composites existed as anatase In the XRD patterns for WO3-fullerene/TiO2, the peaks at 23.15°, 23.61°, 24.37°, 26.61°, 33.33°, 33.65°, 34.01°, and 41.51° 2θ were assigned to diffraction planes of (001), (020), (200), (120), (021), (201), (220), and (221) of monoclinic WO3 phase Due to the small content of tungsten oxide (shown in Table 2), the intension of the peaks are smaller than that of WO3-fullerene, and the other peaks cannot be found in these patterns UV-vis diffuse reflectance spectroscopy The UV-vis absorption spectra of the samples are shown in Figure 5; the illustration is UV-vis absorption spectra of pure TiO2 We can find that TiO 2, WO 3-fullerene, fullerene-TiO , and WO -fullerene/TiO composites have great absorption at ultraviolet region, but the absorption edge of TiO2 is approximately 400 nm (Eg = 3.2 eV) When at the visible region, WO3-fullerene, fullerene/TiO2, and WO3-fullerene-TiO2 composites have good absorption; this is also means that these composites have great photocatalytic activity under visible light irradiation Because WO has a relatively small band gap (2.6 eV to approximately 3.0 eV), WO have Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page of 11 A 1000 WW (c) 800 Relative intensity W WW A W AA A A AA A (a) WO3-fullerene (b) fullerene-TiO2 600 (c) WO3-fullerene/TiO2 (b) 400 200 W W W W W (a) 10 20 30 40 50 theta ( ) Figure XRD patterns of WO3-fullerene (a), fullerene-TiO2 (b), and WO3-fullerene/TiO2 (c) Figure UV-vis absorption spectra of photocatalysts 60 70 80 Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page of 11 photocatalytic activity at visible region, from the wavelength at 400 to 443 nm And fullerene also acted as a photosensitizer, so that WO3-fullerene has good adsorption at visible region In the case of fullerene-coupled TiO2, fullerene acted as a photosensitizer, which could be excited to inject electrons into the conduction band of TiO Because of the synergistic reaction of WO , fullerene, and TiO2, the adsorption effect of WO3-fullerene/TiO2 is good at visible region [25,26] Photocatalytic activity of samples Two steps are involved in the photocatalytic decomposition of dyes, the adsorption of dye molecules, and their degradation After adsorption in the dark for h, all the samples reached adsorption-desorption equilibrium [27] Figure shows the adsorptive and degradation effect of photocatalysts for MO In the adsorptive step, TiO , WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 composites showed different adsorptive effects with WO3-fullerene having the best adsorptive effect, and the adsorptive effect of pure TiO2 was the lowest This is because fullerene can enhance the adsorption effect WO3-fullerene has the largest BET surface area, which will affect the adsorptive effect The decolorization efficiencies of WO3 -fullerene, fullerene-TiO , and WO3 fullerene/TiO composites were 45.17%, 32.12%, and 23.41%, respectively These results are consistent with the BET surface areas In the degradation step, Figure shows the results of TiO2, WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 composites degradation MO solutions under visible light The relative yields of the photolysis products formed under different irradiation time conditions are shown for the products The dye concentration was 1.0 × 10 -5 mol/l, and the absorbance decreased with increasing irradiation time This suggests that the light transparency of the dye concentration was increased greatly by the photocatalytic degradation effect The effect of the high crystallinity of the anatase phase on the photocatalytic degradation of dye was shown Under visible light irradiation, TiO cannot depredate MO molecules, but WO -fullerene, fullerene-TiO , and WO3-fullerene/TiO2 composites have good photocatalytic activity Comparing these three samples, WO3-fullerene/TiO composite has the best degradation effect, which is due to the synergistic reaction of WO3, fullerene, and TiO2 Figure presents the corresponding -ln(C/C ) vs t plots at to 120 irradiation time The photodegradation followed first-order kinetics The kinetics can be expressed as follows: -ln(C/C0) = kappt, where kapp is the apparent reaction rate constant, and C0 and C are the initial concentration and the reaction concentration of MO, respectively Table shows the rate constant values (kapp) of pure TiO2, WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 composites for the degradation of 1.2 1.0 Absorbance Adsorption 0.8 Photo-degradation 0.6 TiO2 WO3-fullerene 0.4 fullerene-TiO2 WO3-fullerene/TiO2 -120 -110 50 100 Irradiation time (min) Figure Decolorization effect on MO of pure TiO2, WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO2 Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page of 11 0.6 TiO2 0.5 WO3-fullerene TiO2-fullerene -ln (c/co) 0.4 WO3-fullerene/TiO2 0.3 0.2 0.1 0.0 20 40 60 80 100 120 Irradiation time (min) Figure Corresponding -ln(C/C0) vs t plots the MO solution The kapp value of the WO3-fullerene/ TiO2 sample is the largest, which is in accord with the photocatalytic activity Fullerene-TiO2 has a better degradation effect than pure TiO2 because fullerene is an energy sensitizer that improves the quantum efficiency and increases charge transfer [28,29] The TiO deposited on the fullerene surface can retain its photodegradation activity In the fullerene-coupled TiO2 system, the photocatalytic activities were enhanced mainly due to the high efficiency of charge separation induced by the synergistic effect of fullerene and TiO In the case of fullerene-coupled TiO2, hole and electron pairs were generated and separated on the interface of fullerene by visible light irradiation The level of the conduction band in TiO was lower than the reduction potential of fullerene Therefore, the photogenerated electron can transfer easily from the conduction band of fullerene to a TiO2 molecule with an interaction between fullerene and TiO Simultaneously, the holes in the valence band (VB) of TiO2 can transfer directly to fullerene because the VB of TiO2 matches well with fullerene The synergistic effect fullerene and TiO2 both promoted the separation efficiency of the photogenerated electron-hole pairs, resulting in the high photocatalytic activity of fullerenehybridized TiO samples In this case, the fullerenecoupled TiO system improved the reaction state [30-32] Therefore, the fullerene-coupled TiO has photocatalytic activity under visible light Figure shows a schematic diagram of the separation of photogenerated electrons and holes on the fullerene-TiO2 interface WO -fullerene also has a barrier degradation effect than pure TiO2 , due to the same reason as fullereneTiO2 system From Figure and Table 2, we can find that the kapp of WO3-fullerene is 2.86 × 10-3, which is larger than that of fullerene-TiO2 (1.52 × 10-3) This is because, with the band gap of WO being relatively small, electrons will obtain energy to jump onto the conduction band and become free electrons named photoelectrons when under visible light irradiation In this system hole and electron pairs were also generated and separated on the interface of fullerene Fullerene is acted as photosensitize These electron-hole pairs can recombine or diffuse to the surface where they can initiate redox reactions with surface species, so the degradation effects of TiO2-fullerene and WO3-fullerene/TiO2 were limited At WO -fullerene/TiO system, the photocatalytic activities were enhanced mainly due to the high efficiency of charge separation induced by the synergistic effect of fullerene, WO3, and TiO2 Because of the least band gap of fullerene (1.6 to 1.9 eV), hole and electron pairs were generated and separated on the interface of fullerene easily by visible light irradiation, and the Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 Page 10 of 11 Figure Schematic diagram of the separation of photogenerated electrons and holes on the WO3-fullerene/TiO2 interface electron can transfer easily from the CB of fullerene to a TiO2 molecule and, simultaneously, the holes in the VB of TiO2 can transfer directly to fullerene because both the conduction band (CB) and the valence band (VB) of WO3 were higher than the CB and VB of TiO2 and fullerene When the hole and electron pairs were also generated and separated on the interface of WO3, electrons at the CB of WO3 migrated to CB of TiO2 and fullerene, and holes at the VB of WO migrated to VB of TiO2 and fullerene [33] This can allow the transfer of photogenerated electrons facilitating effective charge separation and decreased the rate of recombination about the electron-hole pairs Fullerene also acts as the adsorb facient and increases the surface area of compounds which can increase the adsorption effect for samples, adsorbed more O and dye molecules, and make sure this systems take full advantage of yield oxidizing species Figure is the schematic diagram of the separation of photogenerated electrons and holes on the WO3-fullerene/TiO2 interface Electrons and holes were used to produce the hydroxyl radicals (OH·) and superoxide ions (O ·- ) Oxidative degradation of azo dyes occurs by the attack of hydroxyl radicals and superoxide ions, which are the highly reactive electrophilic oxidants Due to the efficiency of hydroxyl radicals and superoxide ions, azo dyes were decompounded to CO , H O, and inorganic Conclusions This study examined the preparation and characterization of WO3-fullerene, fullerene-TiO2, and WO3-fullerene/TiO The BET surface area of pristine fullerene was higher than that of the WO3-fullerene/TiO2 composite XRD revealed the WO3 structure and anatase TEM showed that TiO particles with some agglomerates were dispersed over the surface of fullerene together with WO3 particles In UV-vis absorption, spectra samples have shown a great adsorption at visible region Fullerene-TiO has a good photodegradation effect under visible light irradiation, due to the photosensitivity, and enhances the BET surface area effect of fullerene The WO -fullerene/TiO composite showed the best photocatalytic degradation activity of the MO solution under visible light irradiation This was attributed to the three different effects between the photocatalytic reactions of the supported TiO2, to the energy transfer Meng et al Nanoscale Research Letters 2011, 6:459 http://www.nanoscalereslett.com/content/6/1/459 effects of fullerene and WO , such as electrons and light, and to the separation effect in this system Authors’ contributions The work presented here was carried out in collaboration between all authors WCO an MZD defined the research theme MZD and WCO designed methods and experiments, and experiments and wrote the paper LZ carried out the laboratory experiments JGC and CYP analyzed the date, interpreted the results All authors have contributed to, seen and approved the manuscript Competing interests The authors declare that they have no competing interests Received: April 2011 Accepted: 20 July 2011 Published: 20 July 2011 References Dvoranova D, Brezova V, Mazur M, Malati MA: Investigations of metaldoped titanium dioxide photocatalysts Appl Catal B-Environ 2002, 37:91 Tseng IH, Chang WC, Wu JCS: Photoreduction of CO2 using sol-gel derived titania and 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TiO2 thin films J Mater Chem 2007, 17:1361 32 Zhang FJ, Oh WC: Photoelectrocatalytic properties of Mo-CNT/TiO2 composite electrodes under visible light Asian J Chem 2011, 23:372 33 Wang Y, Cai L, Li YY, Tang Y, Xie CS: Structural and photoelectrocatalytic characteristic of ZnO/ZnWO4/WO3 nanocomposites with double heterojunctions Physica E 2010, 43:503 doi:10.1186/1556-276X-6-459 Cite this article as: Meng et al.: Preparation, characterization and photocatalytic behavior of WO3-fullerene/TiO2 catalysts under visible light Nanoscale Research Letters 2011 6:459 Submit your manuscript to a journal and benefit from: Convenient online submission Rigorous peer review Immediate publication on acceptance Open access: articles freely available online High visibility within the field Retaining the copyright to your article Submit your next manuscript at springeropen.com ... conduction band (CB) and the valence band (VB) of WO3 were higher than the CB and VB of TiO2 and fullerene When the hole and electron pairs were also generated and separated on the interface of WO3,... Preparation, characterization and photocatalytic behavior of WO3-fullerene/TiO2 catalysts under visible light Nanoscale Research Letters 2011 6:459 Submit your manuscript to a journal and benefit... effect of fullerene, WO3, and TiO2 Because of the least band gap of fullerene (1.6 to 1.9 eV), hole and electron pairs were generated and separated on the interface of fullerene easily by visible